1. Field of the Invention
The present invention relates to composite vibration devices that support a variety of vibrating members, with little influence on the vibration characteristics of the vibrating members. More particularly, the present invention relates to composite vibration devices, in which piezoelectric elements, electrostrictive elements, or other suitable elements are used as vibrating members.
2. Description of the Related Art
Conventionally, piezoelectric vibrating components have been widely used in resonators, filters, and other electronic components. For example, piezoelectric resonators use various vibration modes to obtain target resonant frequencies. As these vibrating modes, a thickness longitudinal vibration, a thickness-shear vibration, a length vibration, a width vibration, an extension vibration, a bending vibration, and other modes are known.
In such piezoelectric resonators, the supporting structures thereof vary with the type of vibration modes. Energy-trap piezoelectric resonators using a thickness longitudinal vibration and a thickness-shear vibration can be mechanically supported at both ends thereof. FIG. 34 shows an example of an energy-trap piezoelectric resonator using a thickness-shear vibration. In a piezoelectric resonator 201, a resonant electrode 203 is provided on the top surface of a piezoelectric plate 202 having a strip-like configuration and a resonant electrode 204 is provided on the bottom surface thereof and is disposed opposite to the resonant electrode 203. The resonant electrodes 203 and 204 are opposed to each other at the approximate center in the lengthwise direction of the piezoelectric strip 202. The opposing portion thereof defines an energy-trap piezoelectric vibrating section. As a result, vibration is trapped in the piezoelectric vibrating section. Thus, the piezoelectric resonator 201 can be mechanically supported at its ends without influencing the vibration of the piezoelectric vibrating section.
In the energy-trap piezoelectric resonator 201, however, although vibrating energy is trapped in the piezoelectric vibrating section, a vibration attenuating section requiring a relatively large space must be provided outside the piezoelectric vibrating section. Consequently, for example, the length of the piezoelectric resonator strip 201 using a thickness-shear mode must be increased.
On the other hand, in piezoelectric resonators using a length vibration, a width vibration, an extension vibration, and a bending vibration, it is not possible to produce an energy-trap piezoelectric vibrating section. Thus, in order to prevent any influence on the resonant characteristics, a metal spring terminal is utilized to allow the terminal to be in contact with a node of vibration of the piezoelectric resonator. This arrangement permits the formation of a supporting structure.
In Japanese Unexamined Patent Application Publication No. 10-270979, a bulk acoustic wave filter 211 is provided as shown in FIG. 35. In the bulk acoustic wave filter 211, a plurality of films is stacked on a substrate 212. In other words, a piezoelectric layer 213 is provided in the multi-layered structure. On the top and bottom of the piezoelectric layer 213, stacked electrodes 214 and 215 are provided to define a piezoelectric resonator. In addition, on the bottom of the piezoelectric resonator, films made of silicon, polysilicon, or other suitable material are provided to define an acoustic mirror 219 having a multi-layered structure composed of a top layer 216, a middle layer 217, and a bottom layer 218. In this case, the acoustical impedance of the middle layer 217 is higher than the acoustical impedances of the top layer 216 and the bottom layer 218. The acoustic mirror 219 blocks the propagation of vibration produced by the piezoelectric resonator to the substrate 212.
In addition, an acoustic mirror 220 having the same structure is stacked on the upper portion of the piezoelectric resonator. A passivation film 221 is provided on the acoustic mirror 220. The passivation film 221 is made of a protective material such as epoxy, SiO2, or other suitable material.
In such a conventional energy-trap piezoelectric resonator, a vibration attenuating section must be provided on the outside of the piezoelectric vibrating section. Thus, although the resonator can be mechanically supported with an adhesive, the size of the piezoelectric resonator 201 is increased.
Furthermore, non-energy-trap piezoelectric resonators using a length vibration mode and an extension vibration mode do not need a vibration attenuating section. However, the resonant characteristics of the piezoelectric resonator deteriorate when the resonator is fixed and supported with an adhesive, solder, or other fixing material. As a result, since the resonator must be supported by a spring terminal, the supporting structure is complicated and requires many components.
As described above, in the bulk acoustic wave filter disclosed in Japanese Unexamined Patent Application Publication No. 10-270979, the plurality of films is stacked on the substrate 212 to define the piezoelectric resonator and the acoustic mirror 219 acoustically isolates the piezoelectric resonator from the substrate. Thus, the piezoelectric resonator is acoustically isolated and supported by the acoustic mirror 219 having the multi-layer structure on the substrate 212.
However, in the bulk acoustic wave filter 211, on the substrate 212, many layers must be stacked to form the multi-layer structure defining the bottom acoustic mirror 219, the piezoelectric resonator, and the piezoelectric filter, and also, many layers must be stacked to define the top acoustic mirror 220. Additionally, on the top portion of the filter, the passivation film 221 must be arranged. As a result, the structure of the filter is complicated, and the vibration mode of the piezoelectric resonator is restricted because the resonator is defined by the multi-layer structure.
As mentioned above, conventionally, when a vibration source such as a piezoelectric resonator is supported without deteriorating the vibration characteristics, there are restrictions on the vibration mode of the resonator, the component size increases, and the structure is complicated.
To overcome the above-described problems, preferred embodiments of the present invention provide a composite vibration device that is supported by a relatively simple structure using a vibrating member producing a variety of vibration modes, with little or no influence on the vibration characteristics of the vibrating member.
According to a first preferred embodiment of the present invention, a composite vibration device includes a vibrating member as a vibration producing source, the vibrating member being made of a material having a first acoustical impedance Z1, first and second reflecting layers connected to respective sides of the vibrating member, each of the layers being made of a material having a second acoustical impedance Z2 which is lower than the first acoustical impedance Z1, and supporting members, each of which is made of a material having a third acoustical impedance Z3 which is higher than the second acoustical impedance Z2, the supporting members being connected to sides of the reflecting layers opposing the sides thereof connected to the vibrating member, In this composite vibration device, vibrations propagated from the vibrating member to the reflecting layers are reflected at the interfaces between the reflecting layers and the supporting members.
According to another aspect of the present invention, a composite vibration device includes a vibrating member as a vibration producing source, the vibrating member being made of a material having a first acoustical impedance Z1, a reflecting layer connected to a side of the vibrating member, the reflecting layer being made of a material having a second acoustical empedance Z2 which is lower than the first acoustical impedance Z1 and a supporting member, the s upporting member being made of a material having a third acoustical impedance Z3 which is higher than the second acoustical impedance Z2, the supporting member being connected to the side of the reflecting layer opposing the side there of connected to the vibrating member. In this composite vibration device, the vibration propagated from the vibrating member to the reflecting layer is reflected at the interface between the reflecting layer and the supporting member.
The ratio Z2/Z1 of the second acoustical impedance Z2 with respect to the first acoustical impedance Z1 is preferably about 0.2 or less, and more preferably about 0.1 or less.
In addition, the ratio Z2/Z3 of the second acoustical impedance Z2 with respect to the third acoustical impedance Z3 is preferably about 0.2 or less, and more preferably about 0.1 or less.
Further, the vibrating member is preferably defined by an electromechanical coupling conversion element. Also, the electromechanical coupling conversion element is defined by a piezoelectric element or an electrostrictive element.
The composite vibration device of the present preferred embodiment of the invention may also preferably include a third reflecting layer, a second vibrating member, a fourth reflecting layer, and a third supporting member, which are connected, in this order, to a side of at least one of the first and second supporting members opposing the side thereof connected to at least one of the first and second reflecting layers.
According to a second preferred embodiment of the invention, a composite vibration device includes first and second vibrating members defining vibration producing sources, each of the vibrating members being made of a material having a first acoustical impedance Z1, first to third reflecting layers, each of which is made of a material having a second acoustical impedance Z2 which is lower than the first acoustical impedance Z1, and first and second supporting members, each of which is made of a material having a third acoustical impedance Z3 which is higher than the second acoustical impedance Z2. In this composite vibration device, the first supporting member, the first reflecting layer, the first vibrating member, the second reflecting layer, the second vibrating member, the third reflecting layer, and the second supporting member are connected in this order, and vibrations produced by the first and second vibrating members are reflected at the interface between the first reflecting layer and the first supporting member, at the interface between the third reflecting layer and the second supporting member, and at the interfaces between the second reflecting layer and the first and second vibrating members.
In addition, the reflecting layers may be formed by stacking a plurality of layers made of materials having different acoustical impedances.
In addition, when the wavelength of vibrations produced by only one vibrating member is represented by xcex, the distances from the interfaces between the reflecting layers and the vibrating member to the interfaces between the reflecting layers and the supporting members are preferably in a range of nxc2x7xcex/4xc2x1xcex/8, in which the symbol n represents an odd number.
In the composite vibration device according to preferred embodiments of the present invention, when the symbol A represents the direction of vibration displacement of the vibrating member, the symbol B represents the direction of vibrations propagating through the vibrating member, and the symbol C represents the direction of vibrations propagating through the reflecting layers, the directions A, B, and C may be combined in various manners. For example, the directions A, B, and C may be arranged substantially parallel to each other, or the direction A may be substantially parallel to the direction B, whereas the direction B may be substantially perpendicular to the direction C. In contrast, the direction A may be substantially perpendicular to the direction B, whereas the direction B may be substantially parallel to the direction C. Alternatively, the direction A may be substantially perpendicular to the direction B and also the direction B may be substantially perpendicular to the direction C.
According to a third preferred embodiment of the present invention, a composite vibration device includes a vibrating member defining a vibration producing source, the vibrating member being made of a material having a first acoustical impedance Z1, first and second reflecting layers connected to each side of the vibrating member, each of the layers being made of a material having a second acoustical impedance Z2 which is lower than the first acoustical impedance Z1, and supporting members, each of which is made of a material having a third acoustical impedance Z3 which is higher than the second acoustical impedance Z2, the supporting members being connected to sides of the reflecting layers opposing the sides thereof connected to the vibrating member. In this composite vibration device, when the symbol S1 represents the area of the surface of the vibrating member connected to each reflecting layer and the symbol S2 represents the area of the surface of each reflecting layer connected to the vibrating member, the area ratio S2/S1 is preferably about 1 or less, and vibrations propagated from the vibrating member to each reflecting layer are reflected at the interfaces between the reflecting layers and the supporting members.
The ratio Z2/Z1 of the second acoustical impedance Z2 with respect to the first acoustical impedance Z1 is preferably about 0.2 or less, and more preferably about 1.0 or less.
Further, the ratio Z2/Z3 of the second acoustical impedance Z2 with respect to the third acoustical impedance Z3 is preferably about 0.2 or less, and more preferably about 0.1 or less.
In addition, the vibrating member is preferably defined by an electromechanical coupling conversion element. Furthermore, the electromechanical coupling conversion element is preferably defined by a piezoelectric element or an electrostrictive element.
Additionally, the composite vibration device also may preferably include a third reflecting layer, a second vibrating member, a fourth reflecting layer, and a third supporting member, which are connected, in this order, to a side of at least one of the first and second supporting members opposing the side thereof connected to at least one of the first and second reflecting layers.
According to a fourth preferred of the present invention, a composite vibration device includes first and second vibrating members defining vibration producing sources, each of the vibrating members being made of a material having a first acoustical impedance Z1, first to third reflecting layers, each of which is made of a material having a second acoustical impedance Z2 which is lower than the first acoustical impedance Z1, and first and second supporting members, each of which is made of a material having a third acoustical impedance Z3 which is higher than the second acoustical impedance Z2. In this composite vibration device, the first supporting member, the first reflecting layer, the first vibrating member, the second reflecting layer, the second vibrating member, the third reflecting layer, and the second supporting member are connected in this order, and when the symbol S1 represents the area of the surface of the vibrating member connected to each reflecting layer, and the symbol S2 represents the area of the surface of each reflecting layer connected to the vibrating member, the area ratio S2/S1 is about 1 or less, and vibrations produced by the first and second vibrating members are reflected at the interface between the first reflecting layer and the first supporting member, at the interface between the third reflecting layer and the second supporting member, and at the interfaces between the second reflecting layer and the first and second vibrating members.
In addition, the reflecting layers may be formed by stacking a plurality of layers made of materials having different acoustical impedances.
When the wavelength of vibrations produced by only one vibrating member is represented by xcex, the distances from the interface between the reflecting layers and the vibrating member to the interface between the reflecting layers and the supporting members is preferably in a range of nxc2x7xcex/4xc2x1xcex/8, in which the symbol n represents an odd number.
In the composite vibration device according to the fourth preferred embodiment of the present invention, when the symbol A represents the direction of vibration displacement of the vibrating member, the symbol B represents the direction of vibrations propagating through the vibrating member, and the symbol C represents the direction of vibrations propagating through the reflecting layers, the directions A, B, and C may be combined in various manners. For example, the directions A, B, and C may be arranged substantially parallel to each other, or the direction A may be substantially parallel to the direction B, whereas the direction B may be substantially perpendicular to the direction C. In contrast, the direction A may be substantially perpendicular to the direction B, whereas the direction B may be substantially parallel to the direction C, Alternatively, the direction A may be substantially perpendicular to the direction B and also the direction B may be orthogonal to the direction C.